This invention relates to a hydraulic system, and in particular a hydraulic system for an automotive vehicle. The system is of the type including a storage and pressure compensation reservoir and a motor operated pump supplying hydraulic fluid to an adjustable suspension means arranged between the vehicle body and the vehicle axle including a working cylinder having a working piston moving therein and having devices enabling a controlled flow of the pressure medium contained in the piston chamber from one side of the working piston to the other side. The working piston is connected with a piston rod extending from one end of the working cylinder. The suspension system to which the invention relates also includes a separating piston separating the piston chamber from a gas-filled chamber, and a second pressure chamber filled with pressure medium is separated from the gas-filled chamber by means of a movable wall.
The German Pulished Patent Application (DE-OS) No. 24 36 2l6 discloses an adjustable suspension means for vehicles of this general type which has a working cylinder and a piston moving therein and which is provided with devices enabling a pressure medium to flow back and forth in a controlled manner from the one side of the piston to the other. The piston is fastened to a piston rod which protrudes from one end of the working cylinder. This device also includes an outer cylinder which, with the working cylinder, confines an annular reservoir which at least at one end communicates with the working cylinder. The annular reservoir is filled with pressurized gas and pressure fluid with part of the annular reservoir being limited by a flexible wall. Provision is made for connecting a pressure medium line from a component of a level adjusting device of the vehicle to the device. This particular adjustable suspension means has the disadvantage that it requires a pressure medium source of its own and intricate level adjusting valves controlling the admission and discharge of pressure medium in dependence on the respective distance between the vehicle axle and the vehicle body.
Another hydraulic system of the general type to which the invention relates is disclosed in German Patent Specification--DE-PS - No. 30 13 853, which includes an accumulator system for pressurized hydraulic fluid and a plurality of hydraulically operated devices fed by the accumulator system, a hydraulic pump charging the accumulator, and a pressure control unit responding to the accumulator pressure and controlling the charging operation of the hydraulic pump in dependence on two pressure limit values limiting a working pressure range. This hydraulic system is suitable for level adjusting systems and is also suited to simultaneously supply other hydraulically operated components such as hydraulic seat adjusters or window lifters. Accordingly, this hydraulic system is designed such as to automatically shut down less important devices for safety reasons in case of operating troubles, thus allowing the accumulator pressure to be available solely for the device absolutely required for safety such as a servobrake or a power steering system.